Wire rod, steel wire and method for manufacturing same

Abstract

A wire rod according to an embodiment of the present invention comprises, by wt%, 0.94-1.04% of C, 0.9-1.5% of Si, 0.2-0.8% of Mn, 0.2-0.8% of Cr, 0.020-0.105% of Al, 0.0021-0.0205% of N, 2.00-11.00% of Al / N, and the remainder of Fe and other inevitable impurities. A method for manufacturing a wire rod, according to another embodiment of the present invention, comprises the steps of: preparing a billet comprising, by wt%, 0.94-1.04% of C, 0.9-1.5% of Si, 0.2-0.8% of Mn, 0.2-0.8% of Cr, 0.021-0.102% of Al, 0.0021-0.0205% of N, 2.00-11.00% of Al / N, and the remainder of Fe and other inevitable impurities; reheating and hot-rolling the billet; coiling at Acm-80°C to 760°C; cooling from the coiling temperature to 650-620°C, which is the pearlite transformation entry temperature, at 10-20°C / s; and setting and maintaining the conveyor speed at 0.30 m / s or less for 200 seconds or longer for the interval from the cooling temperature to 600-560°C.

Description

Wire rod, steel wire and method of manufacturing the same

[0001] The present invention relates to a wire, steel wire, and a manufacturing method thereof that can be used for bridge cables such as suspension bridges.

[0002] Bridges, such as suspension bridges, use cables that directly or indirectly connect the deck and main towers. While there are differences depending on the cable type, cables are placed in environments where they come into direct or indirect contact with water, so they must be plated after final drawing. Depending on the intended use, zinc or zinc-aluminum (Zn-Al) steel wires are used. The manufacturing process and purpose of the cable steel wires are as follows.

[0003] The strength of steel wires for cables has been continuously increasing from 1660 MPa in the past to 1960 MPa at present. This is because increasing cable strength can reduce the use of materials and shorten the construction period. Accordingly, it is expected that the strength of steel wires for cables will continue to increase through joint development between steel mills, wire manufacturers, and construction companies.

[0004] High-strength steel wire is based on the empirical formula proposed by Embury-Fisher in the 1960s. Strength is increased by increasing alloying elements such as C and Cr, high strength is possible by refining pearlite through isothermal heat treatment, and high strength is possible by increasing the total processing amount in wire drawing and preventing strength reduction during plating. C is an element that is inexpensive and can most effectively improve strength, but there is a limitation because in compositions higher than eutectoid steel, cementite is likely to form at grain boundaries during cooling, which reduces pro-eutectoid workability.

[0005] In addition, Al is being used in parallel with Si for the purpose of removing oxygen from the steel in cable wires, and furthermore, Al is known as an element that suppresses the formation of proeutectoid cementite in hypereutectoid steel, but the increase in its content is limited due to nozzle clogging issues caused by the formation of complex inclusions such as Al2O3 and Al-Si-O.

[0006] Meanwhile, Al combines with N in steel to form AlN, which exists in the austenite grain boundaries, slowing down grain growth and increasing the fresh boundary during the final drawing, so it can be said to be an important element. However, since Al / N control is necessary, securing technology for this is necessary.

[0007] The purpose of the present invention is to provide a wire rod having improved nodule refinement and wire drawing processability through controlling Al / N in a range of 2.00 to 11.00 in high carbon steel having 0.94% or more and multi-stage cooling control during stelmore cooling, and a steel wire having high strength and excellent torsional properties without constant temperature heat treatment.

[0008] According to one embodiment of the present invention, the wire comprises, in weight %, C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.020% to 0.105%, N: 0.0021% to 0.0205%, Al / N: 2.00 to 11.00, the remainder being Fe and other unavoidable impurities.

[0009] In addition, the wire according to one embodiment of the present invention has a density of AlN precipitates having a size of 50 nm or less of 2.4x10 11 dog / mm 2 It could be as follows:

[0010] Additionally, the wire according to one embodiment of the present invention may have an average nodule size of 16㎛ or less.

[0011] Additionally, the wire according to one embodiment of the present invention may have an average pearlite interlayer spacing of 80 nm to 120 nm in a cross-section 1 / 4D (D: diameter) of the wire.

[0012] In addition, the wire according to one embodiment of the present invention may have an average tensile strength of 1600 MPa or more and a cross-sectional reduction ratio of 28% or more.

[0013] According to another embodiment of the present invention, a method for manufacturing a wire rod comprises the steps of: preparing a billet including, in wt%, C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al / N: 2.00 to 11.00, the remainder being Fe and other unavoidable impurities; reheating and hot-rolling the billet; coiling it at Acm-80°C to 760°C; cooling it at 10°C / s to 20°C / s from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature; And it includes a step of maintaining the conveyor speed at 0.30 m / s or less for 200 seconds or more in a temperature range from the cooling temperature to 600°C to 560°C.

[0014] In addition, the method for manufacturing a wire according to one embodiment of the present invention may further include a step of cooling at 5°C / s to 10°C / s to an R / T (reforming tube) charging temperature of 470°C to 440°C after the maintaining step.

[0015] In addition, the method for manufacturing a wire according to one embodiment of the present invention may include a step of reheating and rolling the billet, heating it to 950°C to 1050°C, maintaining it for 90 to 120 minutes, and then rolling it.

[0016] In addition, in the method for manufacturing a wire according to one embodiment of the present invention, the average pearlite interlayer spacing in the cross-section 1 / 4D (D: diameter) of the wire after the maintaining step may be 80 nm to 120 nm.

[0017] In addition, the method for manufacturing a wire according to one embodiment of the present invention may have a tensile strength of 1600 MPa or more and a cross-sectional reduction ratio of 28% or more of the wire after the maintaining step.

[0018] A method for manufacturing a steel wire according to another embodiment of the present invention includes a step of drawing the manufactured wire rod to a total processing amount of 77% to 85% without constant temperature heat treatment after pickling.

[0019] In addition, the method for manufacturing a steel wire according to one embodiment of the present invention may further include a step of performing Zn molten plating.

[0020] According to another embodiment of the present invention, a steel wire has a tensile strength of 2270 MPa or more and a twist (100D. D: diameter) of 26 or more.

[0021] In addition, the steel wire according to one embodiment of the present invention may have a tensile strength of 2130 MPa or more and a twisting strength of 16 or more after Zn hot-dip plating treatment.

[0022] According to the present invention, since it is possible to manufacture a steel wire having excellent high strength and torsional properties without the need for nodule refinement and fresh workability and constant temperature heat treatment, it is possible to reduce CO2 emissions by omitting heat treatment, secure high strength, reduce material quantity, and shorten construction period.

[0023] Figure 1 is a diagram showing the spacing between pearlite layers according to an invention example of the present invention.

[0024] Figure 2 is a diagram schematically illustrating a method for measuring the density of AlN precipitates.

[0025] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0026] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0027] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, unless explicitly defined herein, specific terms should not be interpreted in an overly idealistic or formal sense.

[0028] In addition, the terms "about", "substantially", etc. in this specification are used in the sense of or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure in which exact or absolute numerical values ​​are mentioned to aid understanding of the present invention.

[0029] Unless otherwise specifically stated herein, percentages indicating the content of each element are based on weight.

[0030] First, a wire according to one embodiment of the present invention will be described.

[0031] According to one embodiment of the present invention, the wire comprises, in weight %, C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al / N: 2.00 to 11.00, the remainder being Fe and other unavoidable impurities.

[0032] Hereinafter, the reasons for numerical limitation of the alloy component content in the embodiment of the present invention will be explained.

[0033] C (carbon): 0.94% to 1.04%

[0034] C is the element that can most effectively increase material strength, with a 0.1% C increase resulting in a 100 MPa increase in strength. However, if C is added at less than 0.94%, it is difficult to achieve the product target strength, and if it exceeds 1.04%, the formation of grain boundary cementite and the center segregation disadvantage reduce the drawability, so it is desirable to maintain it below that level. Furthermore, it may be more preferably 0.96% to 1.00%.

[0035] Si (silicon): 0.9% to 1.5%

[0036] Because Si segregates at cementite grain boundaries, it is suitable for preventing strength loss during molten plating. However, if it is less than 0.9%, the strength loss rate is significant, and if it exceeds 1.5%, the formability is poor. Therefore, it is desirable to control it below that level. Furthermore, it may be more preferably 1.20% to 1.30%.

[0037] Mn (manganese): 0.2% to 0.8%

[0038] Mn increases the strength by 20 MPa when increased by 0.1%, and is added for the purpose of providing sufficient hardenability during heat treatment. In the present invention, 0.2% or more is added to remove S in the steel, but since segregation is promoted when added in large amounts, the upper limit of Mn may be 0.8% or less, preferably 0.6% or less, and more preferably 0.3% to 0.5%.

[0039] Cr (chromium): 0.2% to 0.8%

[0040] Cr is an element that has advantages such as an increase in tensile strength of 30-40 MPa through solid solution strengthening when added at 0.1%, and improved wire workability through pearlite refinement. Specifically, because the quenching effect is large, stable pearlite can be formed through transformation nose delay, and pearlite spacing can be refined. However, when added at less than 0.2%, it is difficult to secure tensile strength, and when added at more than 0.8%, coarse eutectic carbides can be formed at grain boundaries, which can cause problems with wire workability. Therefore, it is preferable to control it below that amount. In addition, it can be more preferably 0.5% to 0.7%.

[0041] Al (aluminum): 0.020% to 0.105%

[0042] Al is an element that suppresses the formation of proeutectoid cementite in hypereutectoid steel. Al combines with nitrogen in the steel to form AlN, which exists in the austenite grain boundaries to slow down grain growth and increase the fresh boundary during the final drawing. Therefore, it is added at 0.020% or more. However, if added excessively, nozzle clogging problems may occur due to the formation of composite inclusions such as Al2O3 and Al-Si-O. Therefore, it is desirable to control the upper limit to 0.105%.

[0043] N (nitrogen): 0.0021% to 0.0205%

[0044] N is an element that is effective in improving strength. It combines with Al in steel to form AlN, which exists in austenite grain boundaries, slowing grain growth and increasing the fresh boundary during final drawing. Therefore, it is added in amounts of 0.0021% or more. However, excessive addition results in poor workability, so it is desirable to control the upper limit to 0.0205%.

[0045] Al / N: 2.00 to 11.00

[0046] To improve fresh workability, austenite grain refinement or nodule refinement is necessary. To secure nodules with an average size of 10 to 20 μm, fine formation of AlN precipitates smaller than 50 nm in size is necessary. If the Al / N ratio is less than 2.00, the number of precipitates is small, so nodule refinement does not occur. If it exceeds 11.00, the effect of AlN coarsening does not occur, so it is preferable to control it below that. In addition, it can be more preferably 2.08 to 10.88.

[0047] In addition, the wire according to one embodiment of the present invention has a density of AlN precipitates having a size of 50 nm or less of 2.4x10 11 dog / mm 2 The density of AlN precipitates with a size of 50 nm or less may be 2.4x10 11 dog / mm 2 If the average nodule size exceeds 16㎛, and the average nodule size is large, the stress concentration increases during fresh processing, so the density of AlN precipitates is 2.4x10 11 dog / mm 2 It is desirable to control the average nodule size to 16㎛ or less.

[0048] The remaining component of the present invention is iron (Fe). However, during the typical manufacturing process, unintended impurities from raw materials or the surrounding environment may inevitably be mixed in, and thus cannot be excluded. Since these impurities are readily apparent to anyone skilled in the art of typical manufacturing, their full details are not specifically discussed in this specification.

[0049] In addition, the wire rod according to one embodiment of the present invention may have an average pearlite interlayer spacing of 80 nm to 120 nm in a cross-section of 1 / 4D (D: diameter). It is difficult to control the pearlite interlayer spacing to less than 80 nm due to equipment limitations, and if it exceeds 120 nm, the tensile strength is relatively low, the cross-sectional reduction ratio characteristics are reduced, and the mechanical properties after drawing may also deteriorate. Therefore, it is preferable to control it to less than that.

[0050] In addition, the wire rod according to one embodiment of the present invention may have an average tensile strength of 1600 MPa or more and a cross-sectional reduction ratio of 28% or more. If the tensile strength exceeds 1600 MPa, the life of the die during drawing may be reduced, and the processing speed may not be increased, resulting in poor productivity.

[0051] Next, a method for manufacturing a wire according to one embodiment of the present invention is described.

[0052] A method for manufacturing a wire rod according to one embodiment of the present invention comprises the steps of: preparing a billet including, in wt%, C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al / N: 2.00 to 11.00, the remainder being Fe and other unavoidable impurities; reheating and hot-rolling the billet; coiling it at Acm-80°C to 760°C; cooling it at 10°C / s to 20°C / s from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature; And it includes a step of maintaining the conveyor speed at 0.30 m / s or less for 200 seconds or more in a temperature range from the cooling temperature to 600°C to 560°C.

[0053] The reason for the component range of each alloy composition and the numerical limitation of formula (1) is as described above, and each manufacturing step is described in more detail below.

[0054] The step of preparing the billet can be a normal billet manufacturing process, and the billet is 160x160mm 2 can be manufactured in the size of .

[0055] In addition, the step of reheating and rolling the billet can be performed by a conventional process. For example, after manufacturing a billet having the above-described alloy composition, the billet can be rolled after maintaining it at a heating furnace temperature of 950°C to 1050°C for 90 to 120 minutes for normalizing and forming austenite. If the temperature is maintained below 950°C, there is a problem that the charging time becomes long, and if the temperature is maintained above 1050°C, there is a heating furnace load. Therefore, it is preferable to control it to 950°C to 1050°C. In addition, if it is maintained below 90 minutes, it may be difficult to form central austenite, and if it is maintained above 120 minutes, coarse grain growth may occur.

[0056] Coiling temperature: Acm-80℃ to 760℃

[0057] Because the stelmore is a cooling bed utilizing airflow, the coiling temperature must be kept as low as possible to cool it to the pearlite transformation nose temperature of 650℃ as quickly as possible. The maximum temperature is Acm-80℃. If it is higher, reaching the target temperature is delayed, resulting in uneven pearlite refinement. Furthermore, 760℃ is the minimum temperature for equipment performance. Therefore, it is recommended to control the temperature between Acm-80℃ and 760℃.

[0058] Stelmore cooling control

[0059] The cooling rate can be controlled at 10 to 20°C / s from the coiling temperature to the pearlite transformation nose temperature of 650°C to 620°C. When cooling at less than 10°C / s, uniform pearlite formation is difficult, and when cooling at more than 20°C / s, there are equipment limitations, so it is desirable to control it at a rate lower than that.

[0060] Afterwards, the stelmore cover is completely covered up to the temperature range of 600℃ to 560℃, the conveyor speed is set to 0.30m / s or less, and the corresponding range can be maintained for 200 seconds or more in consideration of pearlite transformation. If the conveyor speed exceeds 0.30m / s, the transformation time is reduced, and low-temperature structures such as martensite are formed, which reduces workability, so it is preferable to control it to below that. In addition, preferably, the conveyor speed can be set to 0.25m / s or less, and the pearlite transformation can be maintained for 200 to 230 seconds.

[0061] After the above-mentioned maintaining step, the average pearlite interlayer spacing in the cross-section 1 / 4D (D: diameter) of the wire may be 80 nm to 120 nm, the tensile strength may be 1600 MPa or more, and the cross-sectional reduction ratio may be 28% or more.

[0062] Afterwards, to improve workability, a cooling step of 5℃ / s to 10℃ / s can be performed until the R / T (reforming tube) is charged (460℃ to 440℃). If it is less than 5℃ / s, the target temperature is not met, and if it exceeds 10℃ / s, there is a restriction on the equipment limit, so it is preferable to control it below that. In addition, it can be preferably 5℃ / s to 8℃ / s.

[0063] The following describes a steel wire and a method for manufacturing the same according to one embodiment of the present invention.

[0064] According to the present invention, a steel wire can be manufactured by drawing the wire rod manufactured by the above manufacturing method at a total processing amount of 77% to 85% without acid washing and constant temperature heat treatment, and the steel wire manufactured thereby can have a drawn wire tensile strength of 2270 MPa or more and a twist (100D. D: diameter) of 26 or more.

[0065] In addition, the method for manufacturing a steel wire according to one embodiment of the present invention may further include a step of performing Zn molten plating treatment, and the tensile strength of the plated wire after the Zn molten plating treatment may be 2130 MPa or more and may be twisted 16 times or more.

[0066] A 100 MPa increase in strength can reduce cable material usage by up to 5%. However, if the tensile strength of the new wire is less than 2270 MPa, cable breaking strength is reduced, which limits cable stability and reduces the reduction in cable material usage. This limits the application of steel wire for cables.

[0067] If the twist of the fresh wire is less than 26 times, it means that there are many internal defects, so even if hot-dip galvanizing is performed, it is difficult to secure the target twist of 16 times or more of the plating wire, which limits its application to steel wire for cables.

[0068] The present invention will be described in more detail through the following examples.

[0069] (Example)

[0070] In the present invention, a sample was manufactured by controlling the Al / N ratio based on the composition system of 0.96C-1.25Si-0.4Mn-0.6Cr in weight% as shown in Table 1 below, and 160x160mm 2 A billet of the size was prepared. Afterwards, the heating temperature was maintained at 990℃ for 80 minutes for low-temperature rolling and coiling. Thereafter, cooling was controlled under the conditions shown in Table 2, and the temperature and holding time for each section are shown in Table 2. In addition, the manufactured wire rod was drawn to approximately 5.0 mm at a speed of 200 m / m using a dry wire drawing machine without LP heat treatment after pickling, and was finished by immersion at a molten plating temperature of 450℃ for approximately 1 minute.

[0071] In addition, the tensile strength, area reduction ratio (RA), drawing amount, number of twists, and occurrence of delamination of the manufactured wire rod and steel wire at room temperature were measured and are shown in Table 3 below.

[0072] For the average pearlite nodule size, the crystal orientation of the ferrite structure is measured using electron backscatter diffraction (EBSD) equipment on the cross-section of the wire, and then the case where the misorientation of adjacent ferrite crystals is 10° or more is defined as the nodule boundary, and the size of the crystal grain formed by the boundary line drawn at this time is measured, and the average of three arbitrary points is shown.

[0073] In addition, in the case of measuring the tensile strength of the wire, a 40 cm long piece was cut from the 2 rings (circumference: 3.2 m) at the rear end of the coil and a tensile test was performed. The tensile speed (cross head speed) was 70 m / m and the length of the balanced section was 30 cm. The diameter before the tensile test was measured using a stereo projector, and the diameter of the necked part after the tensile test was used to measure the cross-sectional reduction ratio (= 1 - (after tensile test / before acceptance test)^2) * 100).

[0074] In the case of measuring the tensile strength of the steel wire according to the present invention, the tensile test specimen length is 40 cm, the tensile speed (cross head speed) is 100 m / m, and the equilibrium length is 30 cm, which is the same as the wire rod. The elongation is determined as the % of the elongated length compared to the initial length of 30 cm, and in the case of torsion, the back load is load (kg) x 0.008, the length is 100D (D: diameter), and the number of fractures is confirmed while rotating the non-fixed chuck in the same direction while fixing one chuck.

[0075] The density of AlN precipitates less than 50 nm was determined using the following method.

[0076] As shown in Fig. 2, the manufactured wire (A) was mechanically milled to the center, then the center was cut off and polished to manufacture a specimen (B). After electropolishing, a film was deposited to extract only AlN precipitates for the observation surface microstructure (C) where cementite and grain boundaries were formed, and the precipitates were analyzed using a transmission electron microscope (TEM) (D). The polishing solution was 3% picric acid, and the film was carbon (C). The TEM analysis field of view was 500 nm x 500 nm, and the number of precipitates was confirmed by measuring in a total of 20 random areas and deriving an average value.

[0077] The spacing between pearlite layers was confirmed using a scanning electron microscope (SEM). A total of 10 measurements were taken at a magnification of x5000, selecting a region perpendicular to the incident beam, and the average was taken.

[0078] CSiMnCrAlNAl / NInvention Example 10.961.250.40.60.0220.00215.44Invention Example 20.961.250.40.60.0210.00522.10Comparative Example 10.961.250.40.60.0230.01101.09Comparative Example 20.961.250.40.60.0220.02200.52Invention Example 30.961.250.40.60.0440.002110.88Invention Example 40.961.250.4 0.60.0430.00504.46Invention Example 50.961.250.40.60.0430.01032.17Comparative Example 30.961.250.40.60.0420.02021.08Comparative Example 40.961.250.40.60.0610.002512.67Invention Example 60.961.250.40.60.0620.00506.44Invention Example 70.961.250.40.60.0620.01003.22Comparative Example 50.961.25 0.40.60.0630.02201.49Comparative Example 60.961.250.40.60.0810.002219.11Invention Example 80.961.250.40.60.0810.00537.93Invention Example 90.961.250.40.60.0800.01004.15Invention Example 100.961.250.40.60.0820.02052.08Comparative Example 70.961.250.40.60.1010.002124.97Invention Example 110. 961.250.40.60.1020.005010.59Invention Example 120.961.250.40.60.1010.01025.14Invention Example 130.961.250.40.60.1000.02042.54Comparative Example 80.961.250.40.60.0420.00504.36Comparative Example 90.961.250.40.60.0430.00504.46Invention Example 140.961.250.40.60.0400.00514.07

[0079] Coiling temperature Pearlite transformation entry temperature (℃) Holding time (s) Holding stage end temperature (℃) RT Entry temperature (℃) Nodule size (㎛) Interlayer spacing between pearlite layers (nm) Number of precipitates with a size of 50 nm or less ( / mm) 2 ) Invention example 17906302205804508982.2x10 11 Invention example 280064020558246010891.9x10 11Comparative example 179562521057845023972.2x10 3 Comparative example 2805630230568450251024.0x10 2 Invention example 38006402255804607995.8x10 10 Invention Example 47906202205824659982.0x10 11 Invention example 580563023058645510927.8x10 10 Comparative example 379562523558844525952.1x10 11 Comparative example 479063021558545027942.4x10 11 Invention Example 67806402205804509901.1x10 11 Invention example 78006502305824507899.7x10 10 Comparative example 579064022058646028902.2x10 11 Comparative example 678063021058144022932.4x10 11 Invention example 88006402005844409884.7x10 10 Invention example 98006302205784428851.3x10 11 Invention Example 107956202005834509861.7x10 11 Comparative example 7790640205580452171058.9x10 8 Invention Example 1178063021558046111907.2x10 10 Invention Example 127906502005864528925.8x10 10 Invention Example 1380063022058444712872.2x10 10 Comparative example 8890730210640554191671.2x10 10 Comparative example 9790620105485450101422.1x10 9 Invention example 147906202205824659985.8x10 10

[0080] Tensile strength (MPa) RA (%) Fresh processing amount (%) Tensile strength (MPa) Torsion (times / 100D) Plating Tensile strength (MPa) Delamination occurrence Torsion (times / 100D) Invention example 1 16 20 3 277.5 2 29 0 28 2150 Not occurred 18 Invention example 2 16 30 3 177.5 2 29 0 29 2150 Not occurred 17 Comparative example 1 15 9 0 26 77.5 2 27 0 22 2130 Occurred 0 Comparative example 2 16 10 22 77.5 2 27 0 19 2130 Not occurred Occurrence 3 invention example 3 16 00 29 77.5 2 300 27 2 160 Not occurred 18 invention example 4 16 20 28 77.5 2 310 26 2 170 Not occurred 16 invention example 5 16 10 30 77.5 2 28 0 28 2 140 Not occurred 19 comparison example 3 15 9 0 2 4 77.5 2 2 5 0 18 2 110 Occurrence 0 comparison example 4 16 00 26 77.5 2 6 30 22 14 90 Occurrence 0 invention example 6 16 30 3177.5 2 28 0 29 2 140 Not occurred 20 invention example 7 16 20 29 77.52290302150Not Occurred16Comparative Example516002477.52270242130Not Occurred3Comparative Example616102577.52250242110Not Occurred2Invented Example816502977.52300272160Not Occurred18Invented Example916002977.52280282140Not Occurred17Invented Example1016103077.52270302130Not Occurred18Comparative Example716002677.5227023 2130 Occurrence 0 Invention Example 1116202977.52290282150 Not Occurrence 20 Invention Example 1216303077.52300292160 Not Occurrence 16 Invention Example 1316003077.52270292130 Not Occurrence 17 Comparative Example 814802577.52020121880 Not Occurrence 7 Comparative Example 915402777.52050151910 Not Occurrence 5 Invention Example 1416202884.32380242240 Not Occurrence 14

[0081] Invention Examples 1 to 13 satisfy all composition ranges and Al / N satisfies 2.00 to 11.00. In addition, their coiling temperature is low-temperature coiling of 790°C to 805°C, the pearlite transformation entry temperature is 620°C to 650°C, and the pearlite is maintained for 200 to 230 seconds in the section where pearlite is formed, and the temperature at the end of the holding stage after exiting the stelmore cover is 578°C to 586°C, and it can be confirmed that the temperature upon entering RT is 440°C to 465°C by cooling at a rate of 10°C / s or less. The nodule size is known to be affected by Al / N, and has a size of 11㎛ or less when measured by EBSD (tolerance angle: 10°). As can be seen in Fig. 1, the pearlite interlayer spacing is between 80 and 100nm, and the wire tensile strength is 1600MPa or more, and the cross-sectional reduction ratio is 28% or more.

[0082] The processing evaluation for the coil is shown in Table 3 above. The total permitted processing amount after scale peeling is 77.5%, the fresh tensile strength is 2270 MPa or more, and in a twist test based on 100D (D: wire diameter), it is secured more than 26 times without delamination (right-angle fracture). After maintaining it at 450℃ for a certain period of time and performing Zn melting treatment, it can be confirmed that it has suitable characteristics for cables, such as a tensile strength of 2130 MPa or more in the plating wire and more than 16 times without delamination.

[0083] In contrast, Comparative Examples 1 to 7 have the same composition as Inventive Examples 1 to 13, but do not satisfy the scope of the present invention because the Al / N ratio is less than 2.00 or greater than 11.00. Accordingly, it can be confirmed that Comparative Examples 1 to 7 have a nodule size exceeding 16㎛ even though they undergo the same manufacturing process as Inventive Examples 1 to 13, and the cross-sectional reduction rate is low at less than 28%, confirming that they are affected by the AlN ratio.

[0084] In addition, even when the same amount of fresh processing is applied, it can be confirmed that the tensile strength and number of twists in the comparative examples are lower than those in the inventive examples. In particular, in the plating wires of comparative examples 1, 3, 4, and 7, delamination occurs when twisted, and in the plating wires of comparative examples 2, 5, and 6, even if delamination does not occur, the number of twists is significantly lowered to less than 16, so the effect of AlN can be confirmed.

[0085] Furthermore, changes in the properties of the plating wire due to differences in the process were compared using Invention Example 4 and Comparative Example 8. Specifically, Invention Example 4 and Comparative Example 8 were intended to compare the effects of coiling temperature control, and in the case of Comparative Example 8, the coiling temperature was increased to 890°C. Since the cooling rate hardly changed, the initial temperature of the isothermal transformation was high at 730°C, and when it passed through the cover after being maintained for 210 seconds, the temperature was 640°C, which was higher than that of Invention Example 4, and the temperature when it entered RT was also high at 554°C, which is not suitable for workability. In addition, since the pearlite interlayer spacing is wide at 167㎛, the tensile strength is relatively low at 1480 MPa, the area reduction ratio characteristic is reduced to 25%, and the mechanical properties after drawing are also reduced. In addition, although the plating wire does not delaminate, it can be confirmed that the tensile strength is low at 1880 MPa, making it unsuitable for high-strength applications.

[0086] Comparative Example 9 is a case where the holding time was reduced to 105 seconds and the tensile strength was only 1540 MPa and the cross-sectional reduction rate was only 27%. The physical properties after drawing were not high at 2050 MPa and the torsion value was also low, making it somewhat difficult to apply on site.

[0087] Finally, Invention Example 14 is about the fresh limit, and the fresh processing amount increased by 6.8% compared to Invention Example 4. This is the result of a test to determine whether it is suitable for processing ultra-high-strength products. Even with the increased fresh processing amount, there were no problems during processing, and the tensile strength of the plating wire increased by about 70 MPa to 2240 MPa, but the twist value only decreased by about 2 times.

[0088] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the claims set forth below.

Claims

1. A wire rod containing, by weight %, C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.020% to 0.105%, N: 0.0021% to 0.0205%, Al / N: 2.00 to 11.00, the remainder being Fe and other unavoidable impurities.

2. In claim 1, The density of AlN precipitates with a size of less than 50 nm is 2.4x10 11 dog / mm 2 Lee Ha-in, Seon Jae.

3. In claim 1, Wire with an average nodule size of 16㎛ or less.

4. In claim 1, A wire rod having an average pearlite interlayer spacing of 80 nm to 120 nm in a cross-section of 1 / 4D (D: diameter).

5. In claim 1, Wire rod having an average tensile strength of 1600 MPa or more and a cross-sectional reduction ratio of 28% or more.

6. A step of preparing a billet including C: 0.94% to 1.04% by weight, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al / N: 2.00 to 11.00, the remainder being Fe and other unavoidable impurities; A step of reheating and hot rolling the above billet; Acm-Coiling step at 80℃ to 760℃; A step of cooling from the above coiling temperature to a pearlite transformation entry temperature of 650°C to 620°C at a rate of 10°C / s to 20°C / s; and A method for manufacturing a wire rod, comprising a step of maintaining a conveyor speed of 0.30 m / s or less for 200 seconds or longer in a temperature range from the above cooling temperature to 600°C to 560°C.

7. In claim 6, A method for manufacturing a wire rod, further comprising a step of cooling to a R / T (reforming tube) charging temperature of 470°C to 440°C at a rate of 5°C / s to 10°C / s after the maintaining step.

8. In claim 6, A method for manufacturing a wire rod, wherein the step of reheating and rolling the billet includes the step of heating the billet to 950°C to 1050°C, maintaining the temperature for 90 to 120 minutes, and then rolling the billet.

9. In claim 6, A method for manufacturing a wire, wherein the average pearlite interlayer spacing in a cross-section 1 / 4D (D: diameter) of the wire after the maintaining step is 80 nm to 120 nm.

10. In claim 6, A method for manufacturing a wire rod, wherein the tensile strength of the wire rod after the above-mentioned maintaining step is 1600 MPa or more and the cross-sectional reduction ratio is 28% or more.

11. A method for manufacturing a steel wire, comprising the step of drawing the wire of claim 1 to a total processing amount of 77% to 85% without LP (Lead Patenting) heat treatment after pickling.

12. In claim 11, A method for manufacturing a steel wire, further comprising a step of performing zinc molten plating treatment.

13. A steel wire manufactured by the method of claim 11, having a tensile strength of 2270 MPa or more and a torsion (100D. D: diameter) of 26 or more.

14. A steel wire manufactured by the method of claim 12, wherein the tensile strength of the plated wire after Zn hot-dip galvanizing is 2130 MPa or more and the twisting is 16 or more times.

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